// UUID: b39b0151-8c4c-40d7-9553-878616a87ef9
#include <bits/stdc++.h>
using namespace std;

int main() {
    long long m;
    cin>>m;
    long long n;
    cin>>n;
    long long a;
    long long b;
    long long c;
	vector<long long> allomas(m+1);
    for(long long i=1; i<=n; i++){
        cin>>a>>b;
        if(allomas[a]!=0){if(allomas[a]>b){}
        else{allomas[a]=b;}
        }
        else{allomas[a]=b;}
    }
    a=0;
    b=0;
    c=0;
    for(long long i=1; i<=m; ){
        if(allomas[i]!=0){i=allomas[i];}
        else{
        a=i;
        while(i<=m && allomas[i]==0 ){i++;}
        c=c+(i-a);
        }
    }
    cout<<c-1;









    
}